JPWO2018088344A1 - Wireless communication system and wireless communication method - Google Patents

Abstract

  The wireless communication system includes a wireless device functioning as a base station and a signal processing device, and the wireless device is configured to use a channel of a wireless transmission path between the wireless device and the terminal device based on a wireless signal transmitted from the terminal device. A channel estimation unit that estimates information, a demodulation unit that performs soft decision demodulation on the radio signal based on the channel information estimated by the channel estimation unit, and a terminal device that is a transmission source of the radio signal. A signal switching unit that switches an output destination of the log likelihood ratio obtained by the decision demodulation to one of a first path through a decoding unit that decodes the log likelihood ratio and a second path not through the decoding unit; A transmission unit that transmits a signal output from the first path or the second path to the signal processing device.

Description

The present invention relates to a wireless communication system and a wireless communication method.
This application claims priority based on Japanese Patent Application No. 2016-220513 for which it applied to Japan on November 11, 2016, and uses the content here.

  2. Description of the Related Art Conventionally, in a wireless communication system, particularly a mobile communication system, in order to increase the flexibility of installing a base station, the functions of the base station are shared by two devices, BBU (Base Band Unit) and RRH (Remote Radio Head). , BBU and RRH are considered to be physically separated. As one form of the function division method in BBU and RRH, as shown in FIG. 3, BBU performs a function of MAC (Media Access Control) layer and higher and a coding function which is a part of the function of the physical layer, A function division method in which the RRH performs functions of the physical layer other than the encoding function has been studied (for example, see Non-Patent Document 1). This function division method is called an SPP (Split-PHY Processing) method.

  The method of demodulating a radio signal received at a base station or terminal device does not output the signal bit obtained by demodulation as a bit value of 0 or 1, but the probability that the signal bit is 0 or 1. There is a soft decision demodulation method that outputs a ratio of real values called Likelihood (see Non-Patent Document 2, for example). In the soft decision demodulation method, the output obtained by demodulation is called a log likelihood ratio or LLR (Log Likelihood Ratio). The LLR value generally indicates that the higher the positive value, the higher the possibility that the signal bit is 1. The lower the negative value (the larger the absolute value), the more likely the signal bit is 0. Is high.

  Also, in a mobile communication system, an area covered by one RRH is called a cell, and generally, the cover area overlaps between a plurality of adjacent cells. Therefore, when the terminal device is located near the cell edge (cell edge), a radio signal transmitted / received between the terminal device and a desired RRH and a radio signal transmitted / received between the RRH of the adjacent cell and the terminal device The phenomenon that the radio transmission speed is significantly reduced due to interference with signals becomes a problem. As a means for solving such a problem, for example, as shown in FIG. 4, CoMP (Coordinated Multi-Point transmission / reception) in which adjacent RRHs communicate with each other with respect to terminal devices located near the cell edge. (Inter-base station cooperation) technology has been studied (for example, see Non-Patent Document 3).

  In FIG. 4, the number of linked RRHs is two, but the number of RRHs may be two or more. In future mobile communication systems, RRHs will be installed with high density, and a plurality of RRHs will always perform CoMP on a plurality of terminal devices regardless of whether or not the terminal devices are located at the cell edge. Improvements are also being considered. As one of the CoMP methods in the uplink (direction from RRH to BBU), an LPP obtained by each RRH is transmitted to the BBU after applying the SPP function division method, and obtained by each RRH in the BBU. Techniques for synthesizing LLR are being studied. In this method, whether or not a terminal device that communicates with the RRH is a target of CoMP is notified to the RRH in advance by the MAC layer function of the BBU (see, for example, Non-Patent Document 4).

  FIG. 5 is a diagram illustrating a system configuration example of a wireless communication system 1000 that performs uplink LLR combining signal transmission in a conventional SPP. The wireless communication system 1000 includes a terminal device 91, a plurality of RRHs 92-1 to 92-2, and a BBU 93. Since the RRHs 92-1 and 92-2 have the same configuration, the RRH 92-1 will be described as an example.

The RRH 92-1 includes an RF (Radio Frequency) reception unit 921-1, a channel estimation unit 922-1, and a demodulation unit 923-1. The BBU 93 includes a signal separation unit 931-1, a signal separation unit 931-2, an LLR synthesis unit 932, a decoding unit 933, a decoding unit 934, a decoding unit 935, and a MAC layer function unit 936.
The RF reception unit 921-1 receives a signal transmitted from the terminal device 91. Of the received signals, RF receiving section 921-1 outputs a reference signal to channel estimation section 922-1 and outputs a data signal to demodulation section 923-1. The reference signal is a signal for extracting channel information of the wireless transmission path, and is a signal including a known signal between the terminal device and the RRH. The data signal is a signal to be sent to the BBU and includes a signal bit sequence.

  The channel estimation unit 922-1 performs channel information estimation and reception quality measurement of the wireless transmission path based on the reference signal output from the RF reception unit 921-1. Channel estimation section 922-1 outputs the estimation result of channel information and the measurement result of reception quality to demodulation section 923-1. The demodulator 923-1 performs equalization processing and soft decision demodulation on the received data signal using the channel information estimation result and the reception quality measurement result output from the channel estimation unit 922-1. To obtain the LLR value (soft decision value). The demodulator 923-1 transmits the acquired LLR value (soft decision value) to the BBU 93.

  Based on the CoMP presence / absence information notified from the MAC layer function unit 936, the signal demultiplexing units 931-1 and 931-2 of the BBU 93 change the LLR value of the signal transmitted from the terminal device 91 that is the target of CoMP to the LLR. The data is output to the combining unit 932. On the other hand, the signal separation unit 931-1 outputs the LLR value of the signal transmitted from the terminal device 91 that is not the target of CoMP to the decoding unit 933, and the signal separation unit 931-2 is the terminal device 91 that is not the target of CoMP. The LLR value of the signal transmitted from is output to the decoding unit 934. Here, the CoMP presence / absence information is a flag for notifying whether or not the terminal device 91 belonging to each RRH 92 is a target of CoMP. For example, the flag value is represented by 0 or 1. If the flag value is 0, the terminal device 91 is not subject to CoMP. If the flag value is 1, the terminal device 91 is subject to CoMP. Represents that.

The LLR combining unit 932 combines the LLR values output from the signal separation units 931-1 and 931-2, and outputs the combined LLR value to the decoding unit 935.
The decoding unit 933 restores the signal bit data (hard decision value) by performing a decoding process on the LLR value output from the signal separation unit 931-1. The decoding unit 933 outputs the restored signal bit data to the MAC layer function unit 936.

The decoding unit 934 restores the signal bit data (hard decision value) by performing a decoding process on the LLR value output from the signal separation unit 931-2. The decoding unit 934 outputs the restored signal bit data to the MAC layer function unit 936.
The decoding unit 935 restores the signal bit data (hard decision value) by performing decoding processing on the combined LLR value output from the LLR combining unit 932. The decoding unit 935 outputs the restored signal bit data to the MAC layer function unit 936.

  The MAC layer function unit 936 outputs the signal bit data output from the decoding unit 933, the decoding unit 934, and the decoding unit 935 to the upper layer. Further, the MAC layer function unit 936 determines whether or not the terminal device 91 that is a signal transmission source is a target of CoMP, based on the signal transmitted from the terminal device 91. Specifically, the MAC layer function unit 936 monitors the communication of each of the RRHs 92-1 to 92-2, and the received radio wave intensity of the terminal device 91 belonging to the cells of the RRHs 92-1 and 92-2 is less than the threshold value. In this case, it is determined that the terminal device 91 is a target of CoMP. The MAC layer function unit 936 notifies the RRHs 92-1 and 92-2 and the signal separation units 931-1 and 931-2 of information indicating the presence / absence of a CoMP target.

  As described above, in the base station function division scheme of SPP, a bit error of a radio signal is performed by inputting a more reliable LLR value to the decoding unit 935 and performing decoding using CoMP using LLR combining. And the wireless transmission characteristics can be improved.

Kenji Miyamoto, three others, “Proposal of base station function division method for future wireless access”, IEICE Technical Report, CS2015-15, pp. 33-38, July 2015 Tomoaki Ohtsuki, “Information Communication Basics and Trends [III] -Error Correction Codes”, IEICE Journal, Vol. 90, No. 7, pp. 549-555, July 2007 Hidekazu Taoka, 5 others, "MIMO and inter-cell cooperative transmission / reception technology in LTE-Advanced", NTT DOCOMO Technical Journal, Vol. 18, No. 2, pp. 22-30 Akihiro Saito and five others, "Development of Cooperative Transmission System for Base Stations", Panasonic Technical Journal, Vol. 58, No. 4, pp. 20-25, January 2013

  In conventional SPP signal transmission, all signals transmitted from the RRH 92 to the BBU 93 have LLR values (soft decision values) regardless of whether the signal transmitted from the RRH 92 to the BBU 93 is a target of CoMP. The LLR value is a real value calculated for each information bit (1 bit), and it is necessary to perform quantization with several bits for each LLR value. Therefore, between RRH 92 and BBU 93, a transmission capacity that is the number of information bits that is the number of quantization bits is required. For example, when a radio signal of 1 Gbps (Giga bits per second) is received by the RRH 92 and the number of quantization bits of the LLR value is 5 bits, the transmission capacity between the RRH 92 and the BBU 93 is 5 Gbps. However, signals that are not subject to CoMP need not be transmitted as LLR values. As described above, the signal transmission in the conventional SPP has a problem that the transmission capacity between the RRH 92 and the BBU 93 is unnecessarily increased because a signal that is not subject to CoMP is transmitted as an LLR value.

  In view of the above circumstances, an object of the present invention is to provide a technique capable of reducing the transmission capacity between the RRH and the BBU.

  One aspect of the present invention is a wireless communication system including a wireless device functioning as a base station and a signal processing device, wherein the wireless device is based on a wireless signal transmitted from a terminal device. A channel estimation unit that estimates channel information of a wireless transmission path with a terminal device, a demodulation unit that performs soft decision demodulation on the radio signal based on the channel information estimated by the channel estimation unit, According to a terminal device that is a transmission source of the radio signal, an output destination of the log likelihood ratio obtained by the soft decision demodulation, a first path through a decoding unit that decodes the log likelihood ratio, A wireless communication system comprising: a signal switching unit that switches to any one of a second path that does not pass through a decoding unit; and a transmission unit that transmits a signal output from the first path or the second path to the signal processing device. It is a non.

  In the above wireless communication system, the signal switching unit is configured to obtain a logarithm obtained from the wireless signal transmitted from the terminal device when the terminal device that is the transmission source of the wireless signal is not a target for cooperation between base stations. When the output device of the likelihood ratio is switched to the first route, and the terminal device that is the transmission source of the wireless signal is a target for cooperation between base stations, it is obtained from the wireless signal transmitted from the terminal device. The output destination of the log likelihood ratio may be switched to the second route.

  In the above wireless communication system, the signal processing device includes a notification unit that determines whether a terminal device belonging to the wireless device is a target for inter-base station cooperation, and notifies the wireless device of a determination result, The signal switching unit may determine whether or not a terminal device that is a transmission source of the radio signal is a target for inter-base station cooperation based on the determination result notified from the notification unit.

  One aspect of the present invention is a wireless communication method in a wireless communication system including a wireless device functioning as a base station and a signal processing device, wherein the wireless device is based on a wireless signal transmitted from a terminal device. A channel estimation step of estimating channel information of a radio transmission path between the radio device and the terminal device; and the radio device performs the radio signal on the basis of the channel information estimated in the channel estimation step. A demodulation step for performing soft decision demodulation, and an output destination of the log likelihood ratio obtained by the soft decision demodulation in accordance with a terminal device that is a transmission source of the radio signal by the radio device, the log likelihood ratio A signal switching step of switching between a first path through a decoding unit that decodes the second path and a second path not through the decoding unit, and the wireless device includes the first route Or a transmission step of transmitting a signal outputted from said second path to said signal processing device, a wireless communication method having.

  According to the present invention, it is possible to reduce the transmission capacity between the RRH and the BBU.

1 is a configuration diagram illustrating a system configuration of a wireless communication system 100 according to a first embodiment. It is a block diagram showing the system configuration | structure of the radio | wireless communications system 100a in 2nd Embodiment. It is a figure which shows an example of the function division | segmentation system of SPP. It is a figure which shows the system configuration | structure using a CoMP technique. It is a figure which shows the system structural example of the radio | wireless communications system which performs the signal transmission of the uplink LLR combining in the conventional SPP.

Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is a configuration diagram illustrating a system configuration of a wireless communication system 100 according to the first embodiment. The wireless communication system 100 includes a terminal device 10, a plurality of RRHs (wireless devices) 20-1 to 20-2, and a BBU (signal processing device) 30. In the following description, RRHs 20-1 to 20-2 are described as RRH20 unless otherwise distinguished. The RRH 20 and the BBU 30 function as a base station. The RRHs 20-1 to 20-2 and the BBU 30 are communicably connected by wires (for example, optical fibers or coaxial lines). Since the RRHs 20-1 and 20-2 have the same configuration, the RRH 20-1 will be described as an example.

The RRH 20 includes an RF reception unit 201-1, a channel estimation unit 202-1, a demodulation unit 203-1, a signal switching unit 204-1, a decoding unit 205-1 and a signal multiplexing unit (transmission unit) 206-. 1.
The RF reception unit 201-1 receives a signal (radio signal) transmitted from the terminal device 10. Of the received signals, the RF reception unit 201-1 outputs a reference signal to the channel estimation unit 202-1, and outputs a data signal to the demodulation unit 203-1.

The channel estimation unit 202-1 receives the reference signal output from the RF reception unit 201-1. Channel estimation section 202-1 estimates channel information of the wireless transmission path and measures reception quality based on the input reference signal. Channel estimation section 202-1 outputs the channel information estimation result and reception quality measurement result to demodulation section 203-1.
The demodulator 203-1 receives the data signal output from the RF receiver 201-1 and the channel information estimation result and reception quality measurement result output from the channel estimation unit 202-1. The demodulator 203-1 performs equalization processing and soft decision demodulation on the input data signal using the input channel information estimation result and reception quality measurement result, thereby obtaining an LLR value (soft decision value). get. Demodulation section 203-1 outputs the acquired LLR value (soft decision value) to signal switching section 204-1.

  The signal switching unit 204-1 receives the CoMP presence / absence information notified from the BBU 30 and the LLR value output from the demodulation unit 203-1. The signal switching unit 204-1 switches the output destination of the LLR value based on the input information on the presence / absence of CoMP. Specifically, the signal switching unit 204-1 decodes the output destination of the LLR value obtained from the signal transmitted from the terminal apparatus 10 that is not the target of CoMP to the decoding unit 205-1 (that is, decodes the log likelihood ratio). To the signal multiplexing unit 206-1 (that is, not via the decoding unit), the output destination of the LLR value obtained from the signal transmitted by the terminal device 10 that is the target of CoMP Switch to the second path).

The decoding unit 205-1 receives the LLR value output from the signal switching unit 204-1. The decoding unit 205-1 restores the signal bit data (hard decision value) by performing a decoding process on the input LLR value. Decoding section 205-1 outputs the restored signal bit data to signal multiplexing section 206-1.
The signal multiplexing unit 206-1 receives the LLR value output from the signal switching unit 204-1 and the signal bit data (hard decision value) output from the decoding unit 205-1. The signal multiplexing unit 206-1 generates a multiplexed signal by multiplexing the input LLR value (soft decision value) and the signal bit data (hard decision value), and transmits the generated multiplexed signal to the BBU 30. To do. As shown in FIG. 1, when the number of terminal apparatuses 10 is one, the signal multiplexing unit 206-1 is a multiplexing that includes either an LLR value (soft decision value) or signal bit data (hard decision value). The digitized signal is transmitted to the BBU 30.

The BBU 30 includes a hard / soft separation unit 301-1, a hard / soft separation unit 301-2, an LLR synthesis unit 302, a decoding unit 303, and a MAC layer function unit (notification unit) 304.
The hard / soft separation unit 301-1 and the hard / soft separation unit 301-2 receive the multiplexed signal transmitted from the RRH 20. The hard / soft separation unit 301-1 and the hard / soft separation unit 301-2 separate the received multiplexed signal into signal bit data and an LLR value based on the CoMP presence / absence information notified from the MAC layer function unit 304. The hard / soft separation unit 301-1 and the hard / soft separation unit 301-2 output the signal bit data to the MAC layer function unit 304, and output the LLR value to the LLR synthesis unit 302.

The LLR synthesis unit 302 receives the LLR values output from the hard / soft separation unit 301-1 and the hard / soft separation unit 301-2. The LLR synthesis unit 302 synthesizes the input LLR values and outputs the synthesized LLR value to the decoding unit 303.
The decoding unit 303 receives the combined LLR value output from the LLR combining unit 302 as an input. The decoding unit 303 restores the signal bit data (hard decision value) by performing a decoding process on the input combined LLR value. The decoding unit 303 outputs the restored signal bit data to the MAC layer function unit 304.
The MAC layer function unit 304 determines whether or not the terminal device 10 that is the signal transmission source is the target of CoMP, based on the signal transmitted in advance from the terminal device 10. An existing technique (for example, see Non-Patent Document 4 above) is used to determine whether the terminal device 10 is a target of CoMP. The MAC layer function unit 304 includes information indicating whether or not the terminal device 10 that is the signal transmission source is the target of CoMP, the RRH 20 to which the terminal device 10 that is the signal transmission source belongs, and the hard and soft separation unit 301- 1 and the hard / soft separation part 301-2 are notified in advance.

  According to the radio communication system 100 configured as described above, the RRH 20 acquires a notification indicating whether or not the terminal device 10 belonging to its cell is a target of CoMP from the BBU 30, and based on the acquired notification. A signal transmitted from the terminal device 10 that is not the target of CoMP is transmitted to the BBU 30 as signal bit data instead of the LLR value. Therefore, LLR quantization is not necessary for a signal transmitted from a terminal apparatus 10 that is not the target of CoMP, and the transmission capacity between the RRH 20 and the BBU 30 can be reduced.

<Modification>
In the present embodiment, the number of terminal devices 10 may be plural. In the present embodiment, the number of RRHs 20 may be three or more.
An existing interface may be used for signal conversion used for signal transmission between the RRH 20 and the BBU 30, or an original interface may be used. Further, after RF reception in each RRH 20, processing for receiving a multicarrier signal such as OFDM (Orthogonal Frequency Division Multiplexing) may be performed on the received signal.

(Second Embodiment)
FIG. 2 is a configuration diagram illustrating a system configuration of the wireless communication system 100a according to the second embodiment. The wireless communication system 100a includes a terminal device 10a, a plurality of RRHs 20a-1 to 20a-2, and a BBU 30.
In the second embodiment, the terminal device 10a and the RRH 20a include a plurality of antennas, and perform MIMO (Multiple-Input Multiple-Output) transmission between the terminal device 10a and the RRH 20a. When the radio communication system 100a is configured in this way, each RRH 20a includes a plurality of RF reception units 201-1-1-1 to 201-1-n (n is an integer of 2 or more), and the demodulation unit 203-1 includes The processing to be performed includes signal reception processing using a plurality of antennas. The processes of the channel estimation unit 202-1, the signal switching unit 204-1, the decoding unit 205-1 and the signal multiplexing unit 206-1 are the same as those in the first embodiment.

According to the wireless communication system 100a configured as described above, the same effects as those of the first embodiment can be obtained.
Further, according to the radio communication system 100a, it is possible to reduce the transmission capacity between the RRH 20a and the BBU 30 even in MIMO transmission.

<Modification>
The second embodiment may be modified in the same manner as the first embodiment.

  You may make it implement | achieve all or one part of RRH20, RRH20a, and BBU30 in embodiment mentioned above with a computer. For example, by recording a program for realizing each component included in RRH and BBU on a computer-readable recording medium, and causing the computer system to read and execute the program recorded on the recording medium, RRH, BBU may be realized. Note that the “computer system” herein includes an OS (Operating System) and hardware such as peripheral devices. The “computer-readable recording medium” means a portable medium such as a flexible disk, a magneto-optical disk, a ROM (Read Only Memory), a CD (Compact Disc) -ROM, or a hard disk built in the computer system. Refers to the device. Further, the “computer-readable recording medium” is a program that dynamically holds a program for a short time, like a communication line when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory inside a computer system serving as a server or a client in that case may be included and a program held for a certain period of time. In addition, this program may be for realizing some of the above-described components, and further, the above-described components can be realized in combination with a program already recorded in the computer system. Alternatively, it may be realized using hardware such as PLD (Programmable Logic Device) or FPGA (Field Programmable Gate Array).

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

  The present invention can be used for wireless communication, for example. According to the present invention, it is possible to reduce the transmission capacity between RRH and BBU.

10, 10a, 91 ... terminal devices 20, 20-1, 20-2, 20a, 20a-1, 20a-2, 92-1, 92-2 ... RRH
30, 30a, 93 ... BBU
201-1, 201-2, 201-1-1 to 201-1-n, 201-2-1-201-2-n, 921-1, 921-2 ... RF receivers 202-1 and 202-2 , 922-1, 922-2 ... Channel estimation units 203-1, 203-2, 923-1, 923-2 ... Demodulation units 204-1, 204-2 ... Signal switching units 205-1, 205-2 ... Decoding Units 206-1, 206-2 ... signal multiplexing units 301-1, 301-2 ... hard / soft separation unit 302 ... LLR synthesis unit 303 ... decoding unit 304 ... MAC layer functional units 931-1, 931-2 ... signal separation unit 932 ... LLR synthesis units 933, 934, 935 ... decoding unit 936 ... MAC layer function unit

Claims (4)

A wireless communication system comprising a wireless device functioning as a base station and a signal processing device,
The wireless device includes:
A channel estimation unit that estimates channel information of a wireless transmission path between the wireless device and the terminal device, based on a wireless signal transmitted from the terminal device;
A demodulator that performs soft decision demodulation on the radio signal based on the channel information estimated by the channel estimator;
According to a terminal device that is a transmission source of the radio signal, an output destination of the log likelihood ratio obtained by the soft decision demodulation, a first path through a decoding unit that decodes the log likelihood ratio, A signal switching unit that switches to any one of the second paths not through the decoding unit;
A transmission unit for transmitting a signal output from the first path or the second path to the signal processing device;
A wireless communication system comprising:   When the terminal device that is the transmission source of the wireless signal is not a target for cooperation between base stations, the signal switching unit sets an output destination of the log likelihood ratio obtained from the wireless signal transmitted from the terminal device. When switching to the first path and the terminal device that is the transmission source of the wireless signal is a target for inter-base station cooperation, the output destination of the log likelihood ratio obtained from the wireless signal transmitted from the terminal device The wireless communication system according to claim 1, wherein the wireless communication system is switched to the second route. The signal processing device includes a notification unit that determines whether a terminal device belonging to the wireless device is a target for inter-base station cooperation, and notifies the wireless device of a determination result,
The said signal switching part determines whether the terminal device which is the transmission source of the said radio signal is the object of cooperation between base stations based on the said determination result notified from the said notification part. Wireless communication system. A wireless communication method in a wireless communication system comprising a wireless device functioning as a base station and a signal processing device,
A channel estimation step in which the wireless device estimates channel information of a wireless transmission path between the wireless device and the terminal device based on a wireless signal transmitted from the terminal device;
A demodulation step in which the radio apparatus performs soft decision demodulation on the radio signal based on the channel information estimated in the channel estimation step;
According to the terminal device that is the transmission source of the wireless signal, the wireless device outputs a log likelihood ratio output destination obtained by the soft decision demodulation via a decoding unit that decodes the log likelihood ratio. A signal switching step of switching between one path and a second path not through the decoding unit;
A transmitting step in which the wireless device transmits a signal output from the first route or the second route to the signal processing device;
A wireless communication method.

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